The biosynthetic products of the Engelbreth-Holm-Swarm (
EHS) tumor and the cell-free translation products of
EHS tumor cell
RNA were characterized. Six distinct gene products (three
laminin polypeptides,
entactin/
nidogen, and two
collagen IV chains) comprising the basement membrane matrix were identified by a combination of proteolytic digestion and immunologic techniques. Analysis of the cell-free translation products using
EHS tumor RNA precipitated by anti-
laminin serum confirms earlier evidence that there are at least two B chains encoded by different genes. The anti-
laminin serum also recognized
entactin/
nidogen, which was further identified by specific immunoprecipitation with anti-
entactin serum. Radiolabeled
laminin A chains, synthesized by the
EHS tumor in organ culture, were also identified by the anti-
laminin serum but were not detected among the cell-free translation products of
EHS tumor RNA. Pulse-chase studies of
EHS tumor in organ culture as well as in vitro translation of
EHS tumor RNA suggest that the precursor forms of alpha 1(IV) and alpha 2(IV)
collagen chains are nearly identical in size, with apparent molecular weights of 170,000. The mRNAs encoding these two
polypeptides migrate differently on
sucrose gradients. It is likely that glycosylation and hydroxylation of
collagen IV account for the major differences in molecular weight of mature alpha 1(IV) and alpha 2(IV) chains in the
EHS tumor matrix.